Case 1: Everything fine, when utils.jar used directly.
Case 2: ClassNotFoundException when utils.jar used indirectly.
So, what is the problem?service-utils.jar contains a package named x.y.z which is exactly same with the package name of MyUtils class (so, it is x.y.z.MyUtils)
I think classloading mechanism expected to load MyUtils class under the x.y.z package of service-utils.jar but it is actually located in the x.y.z package of utils.jar. Renaming one of the packages solved problem.
Hope to helps someone else...